This Phase I study explores the feasibility by which the technique of dynamic near-infrared optical tomography (DYNOT) can be employed as an accurate, noninvasive tool to assess tissue perfusion and vascular resistance to aid in the management of resuscitation. Presently there are few noninvasive diagnostic tools, which can elucidate important tissue perfusion and hemodynamic parameters when a victim in acute shock is encountered in the field. The experimental plan calls for the evaluation of three specific aims and involves subjects being managed in an ICU environment. Two of the aims are directed towards implementing a technology development and enhancement effort with the goal of producing more robust numerical methods and to design a versatile, low profile measuring head for use in limb studies. Supplementing this effort will be laboratory studies aimed at identifying the fidelity by which complex physiological signals can be successfully extracted from reconstructed image data. Following optimization of the data collection hardware and numerical methods, we plan to undertake a clinical study aimed at correlating key physiological measures of systemic tissue perfusion, currently obtained through invasive procedures (e.g., Swan Ganz catheterization), to one or more metrics extracted from time-series optical data obtained from the forearms of subjects. These studies are intended to evaluate the hypothesis that implementation of simple hemodynamic provocations (e.g., mild venous occlusion, local tissue heating) together with the capture of time-series optical measures can elicit responses that allow for the extraction of functional metrics that are well correlated to those obtained using invasive methods. If successful, the planned studies are expected to identify a range of technology solutions, based on the framework of DYNOT, that are appropriately geared towards use in field resuscitation and in more complex clinical environments such as the ICU. In the long term, it is anticipated that the developed technology will provide a more safe and effective approach for the evaluation and management of perfusion states in acutely ill patients.